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Polytype analysis of SiC Powders by Raman spectroscopy
Journal of Molecular Structure, 219 (1990) 135-140 Elsevier Science Publishers B.V., Amsterdam - Printed
POLYTYPE ANALYSIS OF Sic
135 in The Netherlands
POWDERSBY RAMANSPECTROSCOPY
K. GOEHLERTI , G. IRMER*, L, MICHALOWSKY’and 3. MONECKE* 1 Sektion Werkstof fwissenschaf t , Bergakadenie Freiberg , PSF 47, 9200 Freiberg (GDR) *Sektion (GDR)
Physik,
Bergakademie
Freiberg,
PSF 47,
9200 Freiberg
SUMMARY The mechanical properties of Sic ceramics are strongly influenced by the polytype composition of the initial SIC powders. Due to overlapping diffraction patterns a classical X-ray analysis of this composition is subjected to large errors, however. On SIC powders of different polytype composition it is demonstrated that Reman spectroscopy is a suitable mean for such an analysis. INTRODUCTION Sic ties
ceramics
for
high
are
promising
temperature
- an excellent melting
- a large
heat
- e small
thermal
- and its
resp.
chemical
sublimation
ties.
expansion
of
of
essential
of
however.
Therefore,
the
powders
as e.g.
temperature,
polytype the
up to high
the
polytype
Due to overlapping
analysis Sic
application
proper-
coefficient,
resistivity
by the is
interesting
capacity,
The microstructure powders,
mechanical
with
hardness,
- a high
influenced
materials
sintered
composition importance
of for
diffraction composition is
which initial
is
strongly
disperse
their
mechanicel
proper-
a classical
X-ray
of
by Raman spectroscopy
the
patterns is
possibility
temperatures.
ceramics,
of
subjected
to large
errors,
a polytype
analysis
of
great
technological
im-
portance. Sic
POLYTYPES AND RAMANSPECTROSCOPY All
valent
Sic
polytype layers
polytypes
consist
interpenetrating may be described of
a threefold
Si
resp.
0022.2860/90/$03.50
two crystallographically of
Si
by a sequence
C atoms,
or a sixfold
of
sublattices which
axis.
0 1990 Elsevier
are
of
Publishers
Each double
perpendicular
stacking
B.V.
equi-
C atoms.
close-packed
stacked
Different
Science
resp.
orders
to are
136
given
by
senting
repeating the
layers
angles
O”,
the
axis
around
layer
plane
sults.
in
Each
of
one Si
are
given
sequences
such
in
and
Table
letters of
with
A,
B and C,
rotation
of
leads
to
and
vice
C atoms
the
a translation
repredouble
within
a 3d close-packed
sequence
by four
the 120’
together
a way that
stacking
atom
60’
of
the
structure
a tetrahedral versa.
re-
surrounding
Typical
examples
Lattice
constants
1.
TABLE 1 Different
polytypes
Ramsdell notation
Stacking sequence
x: 4H 6H 15R 21R
of
Sic Number of atoms per unit cell
AB ABC,... ,... ABCB,...
4 2 8 12
ABCACB , , . .
ABCACBCABACABCB,...
The
number
Si-C
double
ters
C,
N in
the
layers
H resp.
rhombohedral
Ramsdell
within
R denote
the
Brillouin with
the
number
and 2N/3
for
rhombohedral
C
obtained with
zone
zone the by
cated
optical
atoms
in
any
Fig.
the
the
unit
folding
of
const.
1 for
the
three The
each
Sic
and
crystals
of
experimental
These
number
all
case
of
can
be found
in
(ref.
for
the
of let-
resp.
the
1 -
4).
of
and
zones
due This
to
phonon
be
zone
large
them with
the
can
c : N),
optical
phonon of
increa.
the
hexagonal
three
of
hexagonal
Brillouin
6H-Sic. of
center
which
for
Brillouin
and
the
of
extension
polytypes
acoustic
the
(2N
a common large
for
intersections
results
number
is ‘$ for
polytypes.
near
cell
The
direction
contains
polytype.
in
x = k/k - values give the optical max polytype. A detailed description
for
the
hexagonal
phonons
polytypes).
axial
( kmex ;:
tone
for
the
0.7551 0.5048 1.0053 1.5117 3.7700 5.2780
whereas
cubic,
be determined,
of
repeated
indicated
ches
in
can
rhombohedral
Kmax = p
Brillouin
resulting
0.3076 0.3083 0.3073 0.3081 0.3072 0.3073 denotes
sequence,
the
c/nm
structure.
ses
Br@louin s;ri for
notation
a stacking
By Raman spectroscopy
as
, . . .
ABCACBACABCBACBCABACB
a/nm
branthe
indi-
frequencies polytypism
spectra
of
of single
1
bl
k
I-
800 l-
I===
k
-$ 6OCl-5 401 )-
2oc l-
0 rc 0 x=k/k_ Fig. 1. Dispersion curves of the phonons Ci(k) with k in axial direction for (a) different polytypes within the common large Brillouin zone (b) 6H-SiC within its Brillouin zone obtained by the appropriate folding of the common large Brillouin zone EXPERIMENTALPROCEDURE The Raman spectra
of
the Sic
488 nm line
of
the
by a cylindric
samples
heating. tion.
All
The scsttered
mator with photon
an additional means of
are
mode.
diffuse
the
the Raman scattered
slit
of
proved
the
double
to prepare
to from
using
reduce the
predispersion light powders:
by the
strong
in backscattering
it
Different
laser
configura-
a double
the
strong samples
acts
separates
before
onto
monochro-
photomultiplier
powder
was used which
monochromator. the
to avoid
mm and a cooled
In order
excited
beam was focussed
was enalyzed
reflected
from
were
in order
obtained per
prsdispersor
a grating
lens
light
1300 grooves
counting
due to the
The laser
an Ar+-laser.
spectra
powders
background laser
light
as a filter. the
enters
in
the
methods
laser
By light
entrance have been
138
-
compressing
-
led
water,
the
same with
- filling -
into
the
embedding
preparation size
the
powder
into
powder
powder
a glass
being
capillary
in borate
spectra
have been
method.
For powders
second
more stable
the
mixed with
destil-
KBr,
the
The best
a tablet,
melts.
obtained
using
with
method was prefered
tablets.
Samples
and
glass
first,
relatively which
with
the
large
results
a very
simple
small
mean grain
in mechanically
mean grain
size
resulted in spectra similar to those discussed in (
and 986 cm being
strongly
diminished.
cies
below
the
broadened,
Additionally LO-phonon
the
surface
intensity
phonon
of
the
modes with
LO-mode frequen-
one occur.
RESULTS From the it
is
common dispersion
evident
that
are
most suited
the
optical are
grating
given
In the
80/220,
75.9
2 6.2
ned.
The Fig.
Fa,
region
of
the
2a)
shows
2c)
The X-ray composition:
15R and 6.1
than
3b)
frequency
shows
the
region
spectrum
of
steritz,
GDR, (Fig.
Sic
powder
shows
spectrum
the
of
is
of
optical
Whereas
2 8.5
powder
B-SIC
due to
can be seen
(confirming
in the
latter
3C- and 6H-contributions
pure
6H-SIC of
% 15R was obtaigreen,
of
resulted + 2.4
different in the
% 4H, 7.9
(AGH Krakow, Agrochemische only
interpretation clearly
+ 3.2%
Poland)
in contrast
3b)
one
of
Carb.
branches, in Fig.
of
of Besides
a composition
variety
% 6H, 2.7
bution
case
the
spectrum
Poland).
spectrum
that
a rich
this
2 3.7
the
by which
from VEB Kombinat
3a)).
the
acoustic
two peaks
of ‘X-SIC,
with
spectrum of
only
lower
6H and 21R (and
% 4H and 17.1
the
80.4
% 3C.
2b)
analysis
analysis
2 2.6
are
polytypes
FRG, which
Switzerland,
Lonza,
their
the
Fig.
2 6.2
shows
Fig.
by the AGH Krakow,
the X-ray
% 6H, 7.0
Fa,
2.
Kempten,
to
following Fig.
zone
branches
frequency
of
peak).
polytypes.
the
Brillouin
differences
marked by stars
contributions
in contradiction
F1200,
large
the acoustic
frequency
in the Fig.
unidentified
,x-SIC
in the
analysis
in larger
(made available
ghosts
small
small
resulting
spectra
B-SIC powders very
curvss
a polytype
ones.
Typical branch
for
in
to a
Werke Pie-
a 3C-contriof
Fig.
2a))
can be iden-
fied. f
250
150
1000
SO
w /cm4 Fig.
Raman spectra SIC polytypee in 2.
rent
quency region of the common acoustic branch
-
800
900 wlcd
diffethe frelower of
Fig. 3. Raman spectra of different SIC polvtvpes in the frequency region bi the common
optical branches (a) &Sic, VE8 Agrochemische Werks Piesteritz, GDR (b) B-SIC, AGH Krakow, Poland
(a) B-SIC, AGH Krakow, Poland, (b) %-Sic 80/220, Fa. Kempten, FRG, (c),2-Sic, carb, green F1200, Fa, Lonza, Switzerland
CONCLUSION It
could
be shown
for
a polytype
for
a qualitative A quantitative
analysis analysis
gauge
ders.
The in principle
samples,
Raman intensities
reliable
results
of
Raman spectroscopy SIC powders
is
a suitable
mean
and can be used
at
least
only
characte-
characterization.
rized tive
that
yet
is
obtained possible of (ref.
possible e.g.
theoretical
different 6).
by mixing
polytypes
using pure
well
polytype
pow-
calculation
of
does
yield
not
rela-
140
REFERENCES 1 2 3 4
5 6
Crystal Growth and Dislocations, Butterworths A.R. Verma, Scientific Publications, Ltd., London, 1953. L. Patrick, Infrared Absorption in Sic Polytypes, Phys. Rev, 167 (1968) 809-813, D.W. Feldman, J. H. Parker, Jr., W.J. Choyke and L. Patrick, Raman Scattering in 6H Sic, Phys. Rev. 170 (1968) 698-704. 0.~. Feldman, J.H. Parker, Jr., W.J. Choyke and L. Patrick, Phonon Dispersion Curves by Raman Scattering in SIC, Polytypes 3C, 4H, 6H, 15R and 2lR, Phys. Rev. 173 (1968) 787-793. Experimentelle Untersuchung der Ramanstreuung an E. Salje, Kristallpulvern, J, Appl. Cryst. 6 (1973) 442-446. S. Nakashima, Y. Nekakura and 2. Inoue, Structural Identification of SIC Polytypes by Raman Scattering: 27R and 33R Polytypes, 3. Phys. Sot. Japan 56 (1987) 359-364.
POLYTYPE ANALYSIS OF Sic
135 in The Netherlands
POWDERSBY RAMANSPECTROSCOPY
K. GOEHLERTI , G. IRMER*, L, MICHALOWSKY’and 3. MONECKE* 1 Sektion Werkstof fwissenschaf t , Bergakadenie Freiberg , PSF 47, 9200 Freiberg (GDR) *Sektion (GDR)
Physik,
Bergakademie
Freiberg,
PSF 47,
9200 Freiberg
SUMMARY The mechanical properties of Sic ceramics are strongly influenced by the polytype composition of the initial SIC powders. Due to overlapping diffraction patterns a classical X-ray analysis of this composition is subjected to large errors, however. On SIC powders of different polytype composition it is demonstrated that Reman spectroscopy is a suitable mean for such an analysis. INTRODUCTION Sic ties
ceramics
for
high
are
promising
temperature
- an excellent melting
- a large
heat
- e small
thermal
- and its
resp.
chemical
sublimation
ties.
expansion
of
of
essential
of
however.
Therefore,
the
powders
as e.g.
temperature,
polytype the
up to high
the
polytype
Due to overlapping
analysis Sic
application
proper-
coefficient,
resistivity
by the is
interesting
capacity,
The microstructure powders,
mechanical
with
hardness,
- a high
influenced
materials
sintered
composition importance
of for
diffraction composition is
which initial
is
strongly
disperse
their
mechanicel
proper-
a classical
X-ray
of
by Raman spectroscopy
the
patterns is
possibility
temperatures.
ceramics,
of
subjected
to large
errors,
a polytype
analysis
of
great
technological
im-
portance. Sic
POLYTYPES AND RAMANSPECTROSCOPY All
valent
Sic
polytype layers
polytypes
consist
interpenetrating may be described of
a threefold
Si
resp.
0022.2860/90/$03.50
two crystallographically of
Si
by a sequence
C atoms,
or a sixfold
of
sublattices which
axis.
0 1990 Elsevier
are
of
Publishers
Each double
perpendicular
stacking
B.V.
equi-
C atoms.
close-packed
stacked
Different
Science
resp.
orders
to are
136
given
by
senting
repeating the
layers
angles
O”,
the
axis
around
layer
plane
sults.
in
Each
of
one Si
are
given
sequences
such
in
and
Table
letters of
with
A,
B and C,
rotation
of
leads
to
and
vice
C atoms
the
a translation
repredouble
within
a 3d close-packed
sequence
by four
the 120’
together
a way that
stacking
atom
60’
of
the
structure
a tetrahedral versa.
re-
surrounding
Typical
examples
Lattice
constants
1.
TABLE 1 Different
polytypes
Ramsdell notation
Stacking sequence
x: 4H 6H 15R 21R
of
Sic Number of atoms per unit cell
AB ABC,... ,... ABCB,...
4 2 8 12
ABCACB , , . .
ABCACBCABACABCB,...
The
number
Si-C
double
ters
C,
N in
the
layers
H resp.
rhombohedral
Ramsdell
within
R denote
the
Brillouin with
the
number
and 2N/3
for
rhombohedral
C
obtained with
zone
zone the by
cated
optical
atoms
in
any
Fig.
the
the
unit
folding
of
const.
1 for
the
three The
each
Sic
and
crystals
of
experimental
These
number
all
case
of
can
be found
in
(ref.
for
the
of let-
resp.
the
1 -
4).
of
and
zones
due This
to
phonon
be
zone
large
them with
the
can
c : N),
optical
phonon of
increa.
the
hexagonal
three
of
hexagonal
Brillouin
6H-Sic. of
center
which
for
Brillouin
and
the
of
extension
polytypes
acoustic
the
(2N
a common large
for
intersections
results
number
is ‘$ for
polytypes.
near
cell
The
direction
contains
polytype.
in
x = k/k - values give the optical max polytype. A detailed description
for
the
hexagonal
phonons
polytypes).
axial
( kmex ;:
tone
for
the
0.7551 0.5048 1.0053 1.5117 3.7700 5.2780
whereas
cubic,
be determined,
of
repeated
indicated
ches
in
can
rhombohedral
Kmax = p
Brillouin
resulting
0.3076 0.3083 0.3073 0.3081 0.3072 0.3073 denotes
sequence,
the
c/nm
structure.
ses
Br@louin s;ri for
notation
a stacking
By Raman spectroscopy
as
, . . .
ABCACBACABCBACBCABACB
a/nm
branthe
indi-
frequencies polytypism
spectra
of
of single
1
bl
k
I-
800 l-
I===
k
-$ 6OCl-5 401 )-
2oc l-
0 rc 0 x=k/k_ Fig. 1. Dispersion curves of the phonons Ci(k) with k in axial direction for (a) different polytypes within the common large Brillouin zone (b) 6H-SiC within its Brillouin zone obtained by the appropriate folding of the common large Brillouin zone EXPERIMENTALPROCEDURE The Raman spectra
of
the Sic
488 nm line
of
the
by a cylindric
samples
heating. tion.
All
The scsttered
mator with photon
an additional means of
are
mode.
diffuse
the
the Raman scattered
slit
of
proved
the
double
to prepare
to from
using
reduce the
predispersion light powders:
by the
strong
in backscattering
it
Different
laser
configura-
a double
the
strong samples
acts
separates
before
onto
monochro-
photomultiplier
powder
was used which
monochromator. the
to avoid
mm and a cooled
In order
excited
beam was focussed
was enalyzed
reflected
from
were
in order
obtained per
prsdispersor
a grating
lens
light
1300 grooves
counting
due to the
The laser
an Ar+-laser.
spectra
powders
background laser
light
as a filter. the
enters
in
the
methods
laser
By light
entrance have been
138
-
compressing
-
led
water,
the
same with
- filling -
into
the
embedding
preparation size
the
powder
into
powder
powder
a glass
being
capillary
in borate
spectra
have been
method.
For powders
second
more stable
the
mixed with
destil-
KBr,
the
The best
a tablet,
melts.
obtained
using
with
method was prefered
tablets.
Samples
and
glass
first,
relatively which
with
the
large
results
a very
simple
small
mean grain
in mechanically
mean grain
size
resulted in spectra similar to those discussed in (
and 986 cm being
strongly
diminished.
cies
below
the
broadened,
Additionally LO-phonon
the
surface
intensity
phonon
of
the
modes with
LO-mode frequen-
one occur.
RESULTS From the it
is
common dispersion
evident
that
are
most suited
the
optical are
grating
given
In the
80/220,
75.9
2 6.2
ned.
The Fig.
Fa,
region
of
the
2a)
shows
2c)
The X-ray composition:
15R and 6.1
than
3b)
frequency
shows
the
region
spectrum
of
steritz,
GDR, (Fig.
Sic
powder
shows
spectrum
the
of
is
of
optical
Whereas
2 8.5
powder
B-SIC
due to
can be seen
(confirming
in the
latter
3C- and 6H-contributions
pure
6H-SIC of
% 15R was obtaigreen,
of
resulted + 2.4
different in the
% 4H, 7.9
(AGH Krakow, Agrochemische only
interpretation clearly
+ 3.2%
Poland)
in contrast
3b)
one
of
Carb.
branches, in Fig.
of
of Besides
a composition
variety
% 6H, 2.7
bution
case
the
spectrum
Poland).
spectrum
that
a rich
this
2 3.7
the
by which
from VEB Kombinat
3a)).
the
acoustic
two peaks
of ‘X-SIC,
with
spectrum of
only
lower
6H and 21R (and
% 4H and 17.1
the
80.4
% 3C.
2b)
analysis
analysis
2 2.6
are
polytypes
FRG, which
Switzerland,
Lonza,
their
the
Fig.
2 6.2
shows
Fig.
by the AGH Krakow,
the X-ray
% 6H, 7.0
Fa,
2.
Kempten,
to
following Fig.
zone
branches
frequency
of
peak).
polytypes.
the
Brillouin
differences
marked by stars
contributions
in contradiction
F1200,
large
the acoustic
frequency
in the Fig.
unidentified
,x-SIC
in the
analysis
in larger
(made available
ghosts
small
small
resulting
spectra
B-SIC powders very
curvss
a polytype
ones.
Typical branch
for
in
to a
Werke Pie-
a 3C-contriof
Fig.
2a))
can be iden-
fied. f
250
150
1000
SO
w /cm4 Fig.
Raman spectra SIC polytypee in 2.
rent
quency region of the common acoustic branch
-
800
900 wlcd
diffethe frelower of
Fig. 3. Raman spectra of different SIC polvtvpes in the frequency region bi the common
optical branches (a) &Sic, VE8 Agrochemische Werks Piesteritz, GDR (b) B-SIC, AGH Krakow, Poland
(a) B-SIC, AGH Krakow, Poland, (b) %-Sic 80/220, Fa. Kempten, FRG, (c),2-Sic, carb, green F1200, Fa, Lonza, Switzerland
CONCLUSION It
could
be shown
for
a polytype
for
a qualitative A quantitative
analysis analysis
gauge
ders.
The in principle
samples,
Raman intensities
reliable
results
of
Raman spectroscopy SIC powders
is
a suitable
mean
and can be used
at
least
only
characte-
characterization.
rized tive
that
yet
is
obtained possible of (ref.
possible e.g.
theoretical
different 6).
by mixing
polytypes
using pure
well
polytype
pow-
calculation
of
does
yield
not
rela-
140
REFERENCES 1 2 3 4
5 6
Crystal Growth and Dislocations, Butterworths A.R. Verma, Scientific Publications, Ltd., London, 1953. L. Patrick, Infrared Absorption in Sic Polytypes, Phys. Rev, 167 (1968) 809-813, D.W. Feldman, J. H. Parker, Jr., W.J. Choyke and L. Patrick, Raman Scattering in 6H Sic, Phys. Rev. 170 (1968) 698-704. 0.~. Feldman, J.H. Parker, Jr., W.J. Choyke and L. Patrick, Phonon Dispersion Curves by Raman Scattering in SIC, Polytypes 3C, 4H, 6H, 15R and 2lR, Phys. Rev. 173 (1968) 787-793. Experimentelle Untersuchung der Ramanstreuung an E. Salje, Kristallpulvern, J, Appl. Cryst. 6 (1973) 442-446. S. Nakashima, Y. Nekakura and 2. Inoue, Structural Identification of SIC Polytypes by Raman Scattering: 27R and 33R Polytypes, 3. Phys. Sot. Japan 56 (1987) 359-364.